There are two different types of wireless local area network (WLAN). One is an infrastructure mode WLAN which includes an AP and a STA, and the other is an ad hoc mode WLAN which includes only peer STAs. The ad hoc mode WLAN is also called an independent BSS (IBSS).
FIG. 1 shows a conventional infrastructure mode WLAN 100 including two BSSs 112a, 112b which are connected via a distribution system (DS) 114. The BSSs are served by APs 102a, 102b, respectively. In the infrastructure mode WLAN 100, all packets generated by a source STA, such as STA 104a, is first sent to the AP 102a. If the packets are destined outside the BSS 112a, the AP 102a forwards the packets through the DS 114. If the packets are destined to another STA, such as STA 102b, inside the BSS 112a, the AP 102a, after receiving the packets from the source STA 104a, forwards the packets over the air interface to the destination STA 104b in the BSS 112a. Therefore, the same packets are sent twice over the air.
Duplicating such peer-to-peer traffic, (i.e., sending the packets sent from one STA in the BSS to another STA in the same BSS), is an inefficient usage of the wireless medium since any peer-to-peer STA traffic within the BSS requires twice as much bandwidth compared to traffic to or from a STA outside the BSS.
In order to solve this problem, the IEEE 802.11e provides a feature called direct link setup (DLS). With the IEEE 802.11e DLS, a STA first initiates a direct link through the AP and exchanges packets with other STA directly. However, in an IEEE 802.11-based WLAN, STAs within a BSS share the same frequency channel, (i.e., BSS channel), to communicate with each other, and all traffic, (both traffic between a STA and an AP and traffic between STAs), must still be sent over the BSS channel. With this limitation to a single BSS channel, the amount of peer-to-peer traffic in a BSS that can be supported by a single frequency channel is limited by the overall throughput of the BSS. For example, a conventional IEEE 802.11g or 802.11a BSS will not be able to support more than 30-32 spore Mbps at the medium access control (MAC) level (corresponding to a net data rate of 54 Mbps at the physical layer) aggregate throughput.
Furthermore, it is difficult to manage peer-to-peer links in a conventional IEEE 802-11e DLS system. For conventional BSS traffic, (i.e., traffic between STAs and AP), the overall BSS radio range, (where packets can be reliably received), is essentially determined by the AP's radio range. An interference range of the BSS, (where packets cannot be reliably received, but will still create interference to other STAs operating on the same channel), is determined by both the STA's range and the AP's range. However, with DLS, depending on the position of the participating STAs, the interference range associated by a pair of STAs can be quite different to the interference range of the AP. Interaction and impacts of these different interference ranges is complex and has been shown to have large negative effects on network capacity in IEEE 802.11 systems.
Moreover, with conventional IEEE 802.11 systems, peer-to-peer traffic cannot be off-loaded to a different channel than the BSS channel without the involved peer-to-peer STAs losing layer 2 connectivity to the network. Trading off layer 2 connectivity for capacity is not necessarily an attractive alternative, because many of the devices in a WLAN environment need IP connectivity to support various services. For example, a TV receiving a video playback from a DVD player could not download online DVD info, titles, recommendations, or the like during playback. Losing layer 2 connectivity to the AP implies losing the possibility of supporting all services except the on-going peer-to-peer services.
Therefore, it is desirable to provide a method and system for peer-to-peer wireless communication between STAs within the BSS while maintaining layer 2 connectivity and manageability with an AP in the BSS.